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Abstract

Background

Studies on migration often ignore the health and social impact of migrants returning
to their rural communities. Several studies have shown migrants to be particularly
susceptible to HIV infection. This paper investigates whether migrants to rural households
have a higher risk of dying, especially from HIV, than non-migrants.

Methods

Using data from a large and ongoing Demographic Surveillance System, 41,517 adults,
enumerated in bi-annual rounds between 2001 and 2005, and aged 18 to 60 years were
categorized into four groups: external in-migrants, internal migrants, out-migrants
and residents. The risk of dying by migration status was quantified by Cox proportional
hazard regression. In a sub-group analysis of 1212 deaths which occurred in 2000 –
2001 and for which cause of death information was available, the relationship between
migration status and dying from AIDS was examined in logistic regression.

Conclusion

External in-migrants have a higher risk of dying, especially from HIV related causes,
than residents, and in areas with substantial migration this needs to be taken into
account in evaluating mortality statistics and planning health care services.

Background

South Africa has a high level of circular migration with people migrating into urban
areas primarily to look for jobs whilst maintaining contact with their family members
in rural areas [1,2]. Several studies have shown the existence of an association between migration and
the spread of HIV, with migrants being particularly susceptible to HIV infection [3,4]. In an early study in KwaZulu-Natal, people who had recently migrated or changed
their places of residence were three times more likely to be infected with HIV than
residents [5]. A subsequent study on HIV-1 concordance and discordance among migrant and non-migrant
couples in South Africa showed that the direction of spread is not only from returning
migrant men to their rural partners, but also from resident women to their migrant
partners [4]. Therefore both migrants and residents in rural areas are vulnerable to HIV.

Studies on migration often ignore the health and social impact of migrants returning
to their rural communities. Migrants continue to maintain links with their households
in rural areas [5,6] and there is some evidence to suggest that migrants move back to their rural households
for care and support when seriously ill [7]. This phenomenon has been amplified by the emergence of AIDS. A study in Thailand
revealed that the most common place for HIV infected adults to spend the terminal
stage of the illness was in the parental home and the most common caregiver at this
stage was a parent, usually a mother [8]. A study on households' experiences of HIV and AIDS in the study area showed evidence
of return migration of household members working elsewhere if they became ill and
stopped working [9]. However, many rural areas, particularly in sub-Saharan Africa, lack adequate health
facilities and personnel to cater for the sick in these places. Therefore, returning
migrants to these rural communities could influence the burden of disease and mortality
rates locally. This would have implications for health delivery systems in rural areas,
particularly in areas or countries with high prevalence of HIV. South Africa has witnessed
rapid growth in the spread of HIV. It has the highest number of people living with
HIV, and AIDS is the leading cause of death in the country [10,11].

This paper quantifies the overall mortality differentials between migrants and non-migrants
in a rural community in South Africa and investigates more specifically whether returning
migrants have a higher probability of dying from AIDS than non-migrants.

Methods

The study area

The study area is situated in the south-eastern part of the Hlabisa sub-district in
Umkhanyakude, northern KwaZulu Natal, South Africa [12] about 220 km north of the provincial capital of Durban. Health services include a
district hospital and a network of 6 primary health care clinics and two mobile clinic
teams [[10], http://www.africacentre.comwebcite]. In the study area, the crude HIV incidence rate per 100 person-years between 2003
and 2005 was 3.8 [95% confidence interval (CI), 3.2–4.6] in women aged 15–49 years
and 2.3 (95% CI, 1.8–3.1) in men aged 15–54 years [13]. Overall, 21.5% of residents between the ages of 15–49 in the area were HIV-infected,
highest among women aged 25–29 years and men aged 35–39 years [14].

The Demographic Surveillance System (DSS)

Since 2000, a demographic surveillance system known as the Africa Centre Demographic
Information Systems (ACDIS) has been in place in the study site [[12], http://www.africacentre.comwebcite]. The ACDIS maps approximately 11,000 inhabited homesteads in a 435 square kilometre
area, with a total population of approximately 90,000 [[12], http://www.africacentre.comwebcite]. Field workers visit all households in the area twice a year and longitudinal, socio-economic
and demographic information, including the residence and survival status of all household
members is updated. The residential status in ACDIS is in two groups (residents and
non-residents), where "residents," are defined as "individuals who report keeping
their belongings and spending most nights at the surveyed household," and "non-residents"
defined as "individuals whose residence is elsewhere but maintain connections with
the household through periodic visits" [15,16]. Approximately 30% of all household members are non-resident.

Data

Verbal autopsy is routinely conducted on every death notified in the Demographic Surveillance
Area. Verbal autopsy is an epidemiological tool that is used to assess cause of death
in settings where hospital based records are lacking. Trained nurses carry out structured
interviews with close relatives or the main caregiver of the person before they died,
which is then analysed by clinicians to give a cause of death [10]. For the purpose of this study which was carried out in 2006 as part of a master's
course in population-based field epidemiology, verbal autopsy data for 2001 and 2002
was available at the time of the analysis and therefore, the cause of death analysis
was limited to this dataset.

For the overall mortality rates, the data included members of homesteads aged 18 to
60 years in the Demographic Surveillance Area between 1st January 2001 and 31st December 2005. The data was limited to the age group of 18 to 60 years because this
group of people were more likely to be involved in migration http://www.africacentre.comwebcite.

Statistical Analysis

To determine the overall mortality differentials, household members were divided into
four groups: external in-migrants, internal migrants, out-migrants and residents.
People in the Demographic Surveillance Area (DSA) who were resident on 1st January 2001 and remained resident until they either died or were censored at the
last visit date of the fieldworker in 2005 were classified as resident individuals.
People who migrated from outside the DSA into the study area after 1st January 2001 and either died or were still resident in the area at the last visit
date of the fieldworker in 2005 were classified as external in-migrants. Those who
changed residency within the study area after 1st January 2001 were considered as internal migrants. Out-migrants were people who moved
out of the study area during the study period.

To assess the association between migrating into the area and subsequent mortality,
the last migration event that occurred between 1st January 2001 and 31st December 2005 was used. The total person time contribution for each participant was
calculated as the number of days they had been observed as members of their households
starting from the day they entered that migration status in the DSA between 1st January 2001 and 31st December 2005 using their most recent residency episode. The membership episode for
people who did not die during the period was right censored on 31st December 2005 or the date their membership ended whichever was earliest. Where an
individual had more than one residency episode, the most recent was chosen. Whilst
this excluded some residency episodes that did not end with a death, the number of
such individuals was small. The person years for in-migrants starts from the day they
last moved into residency in the area. Household members who were not in the DSA at
any time between 1st January 2001 and 31st December 2005 were not included in the
analyses.

Cause of death analysis

All deaths which occurred in 2001 and 2002 were classified into four groups, external
in-migrant deaths, internal migrant deaths, resident deaths and out-migrant deaths
based on the most recent migration episode before their death and where they died.
Deaths that occurred outside the study area were classified as out-migrant deaths.

To assess the risk of dying from AIDS related complications among the various groups,
a binary variable was generated that took the value 1 if an individual was reported
to have died from AIDS and 0 if not. Both univariate and multivariate logistic regression
models were used to determine the odds of dying from AIDS.

Overall mortality analysis

Cox proportional hazard regression technique was used to quantify the risk of dying
for residents, external in-migrants and internal migrants. The Cox proportional hazard
assumptions were tested and found to be not violated [17,18]. Potential confounders such as age, socio-economic status using number of household
assets [19] and level of education were controlled for in the multivariate model. The household
assets considered were bicycle, block-maker, car, electric stove with oven, electric
hot plate, electric kettle, fridge/freezer, gas cooker, bednet, lorry/tractor, motorcycle/scooter,
radio, car battery, bed, sofa/sofa suit, sewing machine, table/chair, telephone, cell-phone,
television set, video cassette recorder and wheelbarrow. Educational level was grouped
into four based on the grade an individual had completed (Table 1). Mortality rates per 1000 person years were obtained by Kaplan Meier survival analysis
[20].

Table 1. Characteristics of participants in the overall survival analysis

95% confidence intervals for rates, hazard ratios and odd ratios were estimated. Tests
of statistical significance for differences between rates and determining significant
associations between variables were based on the chi-square test [21]. Analysis was done using STATA 10 [22].

Ethics approval for the study was obtained from the Human Research Ethics Committee
of University of the Witwatersrand. Ethics approval for the Africa Centre Demographic
Information System was obtained from the University of KwaZulu-Natal Nelson R. Mandela
School Of Medicine.

Results

Overall mortality over five years

Table 1 gives the background characteristics of participants included in the survival analysis
who were ever resident household members of the cohort between 1st January 2001 and 31st December 2005. In the overall mortality analysis, 3,083 deaths were reported of a
total of 41,517 people between 18 and 60 years of age, 618 deaths among 7,867 external
in-migrants, 255 among 4,403 internal migrants, 310 among 11,476 out-migrants and
1900 deaths were registered among 17,771 residents. The median age of participants
was 28 years with the majority (42.1%) aged 18 to 25 years. The overall mortality
rate over five years was 22.5 per 1000 person years. External in-migrants had the
highest mortality rate, followed by internal migrants, residents and out-migrants
(Table 2). In univariate analysis, a person who moved into the area during this period was
1.60 times more likely to die than someone who was resident, and after adjusting for
other factors, the risk was 1.28. There was no significant difference in the risk
of dying between internal migrants and residents. Out-migrants were 70% less likely
to die than residents. Males were 1.36 times more likely to die during the follow-up
period of five years than females.

Table 2. Relative risk* for univariate and multivariate models for the 5 years survival experience
by migration status

Cause of death

Table 3 gives the characteristics of participants included in the cause of death analysis.
The median age of the 1212 people who died between 1st January 2001 and 31st December 2002 was 35 years (range 18 to 60). Overall, 795 (65.6%) of all deaths were
due to AIDS, about 74% of all female deaths and 57% of all male deaths. There were
116 (15.0%) external in-migrants who died of HIV related causes, 32 internal migrants
(4.0%), 63 (7.7%) out-migrants and 586 (73.7%) were resident individuals. The proportion
of AIDS deaths for external in-migrants and internal migrants was higher than among
residents and out-migrants.

Table 3. Characteristics of participants included in the cause of death analysis

In this sub-group, external in-migrants were 79% more likely to die from AIDS than
residents (Table 4). However, although internal migrants had a higher risk of dying from AIDS compared
to residents, this was not statistically significant. Out-migrants were 9% less likely
to die from AIDS than residents; females were 2.35 times more likely to die from AIDS
than males and people aged 26 to 40 years were 3.47 times more likely to die from
AIDS compared to those aged 18 to 25 years. Members in households with less than 7
assets were 40% more likely to die from AIDS than those with 7 or more assets.

Discussion

External in-migrants were significantly more likely to die than residents, and in
the sub-group analysis they were found to be also more likely to die from AIDS. These
findings are in line with our hypothesis that migrants into rural areas may come back
to rural households when severely ill, and that the higher AIDS mortality is likely
to be related to the age group of migrants, with the pattern lagging the peak of HIV
incidence ages [13].

The findings of a higher overall mortality among in-migrants is consistent with a
similar study conducted in Agincourt DSS on circular labour migration and mortality
in Northeast South Africa [2] in which the annual odds of dying from all causes for returned migrants was between
1.1 and 1.9 times higher than for residents and long-term returned migrants. In this
study, socioeconomic status, gender and age were all associated with the risk of death,
with males at significantly higher risk of dying than females, and people with low
socio-economic status at an increased risk of dying compared to higher socio-economic
individuals. These findings are in line with those of other studies [23-27].

This study could not ascertain the health conditions of the migrants at the time they
moved into the surveillance area, nor their motivation for migration. It is possible
that the decision to migrate for some of the people dying shortly afterwards was not
connected to ill health, although the higher AIDS mortality in the sub-group for whom
cause of death information was available shows that a substantial proportion of deaths
were associated with their chronic condition.

Results from the sub-group analysis of data relating to deaths in 2000 and 2001 showing
that the risk of AIDS mortality is also increased among external in-migrants is consistent
with previous findings of high prevalence of AIDS among migrants and return migration
taking place when the severity of illness experienced by persons with AIDS is substantial
[8]. After becoming ill, migrants may not be able to obtain the additional financial
support or care they need without moving to be with rural household members. There
was however no evidence of a significantly increased risk of dying from AIDS between
residents and internal migrants. Out-migrants from the study area have a lower risk
of dying from AIDS compared to residents, although this did not reach statistical
significance, likely due to the lack of statistical power and small number of events.

Females had a higher risk of dying from AIDS compared to males, which is likely to
be partly due to the higher prevalence of HIV among females than among males [13,14]. The population-based HIV surveillance in the study area in 2004 showed a prevalence
of 27.2% among women aged 15 to 49 years and 13.4% for men aged 15 to 54 years [13,14]. However, although females were more likely to die of AIDS, males had a significantly
higher overall mortality rate than females, most likely due to injuries and accidents.
Other factors associated with AIDS mortality are socioeconomic status and age. Adults
aged 26 to 40 years were most at risk of dying from AIDS, these ages are those of
highest HIV prevalence. A study in Uganda found the highest attributable risk of HIV
associated deaths to be among persons aged 20–39 years and women [28]. Even though individuals with tertiary education had a significantly higher overall
mortality rate than those with grade 1 to 5 education level, they were less likely
to die from AIDS. This could most likely be due to the relatively low HIV prevalence
rate among people with tertiary education as a study from the same population showed
that one additional year of education reduced the hazard of acquiring AIDS by 7% [29].

A possible limitation of the study is the use of verbal autopsy to determine the probable
cause of death. Even though a number of studies have found this instrument to have
a high sensitivity and specificity and to be able to reasonably determine most causes
of deaths [30,31], it is not the gold standard in determining causes of death. A validation of the
verbal autopsy data against hospital records in the study area in 2000 found the sensitivity,
specificity and positive predictive value of the verbal autopsies for non AIDS deaths
of over 90% [10]. For AIDS deaths, the sensitivity, specificity and positive predictive value were
80%, 82% and 85% respectively [10]; however, although this could potentially lead to misclassification of AIDS deaths,
this would be unlikely to be differentially so between external in-migrants and the
other groups. The presence of missing data on education and socioeconomic status is
a possible limitation but this again would be unlikely to differ substantially by
migration category.

Our findings suggest that resource-poor rural areas in Sub-Saharan Africa face an
increased demand for health services as a consequence of severely ill people in-migrating
to the area. Health services thus need to plan for these additional disease burdens
posed by migrants moving into rural areas, whist recognising that most will be returning
residents rather than people completely new to the area. There are also implications
for rural households who may need to respond not only to an additional dependant adult
in the household but also the reduction in household income.

Conclusion

External in-migrants had a higher risk of dying, especially from AIDS, than residents.
It is important that in resource-poor settings with high HIV/AIDS prevalence, disease
burdens and mortality be identified and quantified in order to put in place effective
interventions to better the health conditions of affected populations.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

PW, VH, RW, CH, KB and MLN contributed to the study design, PW extracted and analyzed
the data. PW, VH, RW, CH, KB and MLN participated in the interpretation of data and
writing of the manuscript. All authors approved the final manuscript.

Acknowledgements

The authors would want to thank the field supervisors and fieldworkers working on
the ACDIS. We thank Christian Kyony and the rest of the ACDIS data management team.
We are also grateful to Khin San Tint and Lawrence Mpinga from the Wits School of
Public Health for their support. INDEPTH Network is thanked for awarding a training
fellowship to Paul Welaga for MSc training at the University of Witwatersrand and
supporting the internship at the Africa Centre for Health and Population Studies.
The Africa Centre Surveillance is funded by a grant from the Wellcome Trust, UK, with
grant number GR065377MA.